1. Field of the Invention
The present invention relates to wireless communication technology in a mobile communication system, and more particularly to a method for processing a hand-off.
2. Description of the Related Art
In a mobile communication system, a handoff and/or a handover function, which enables a mobile terminal to maintain communication without interruption, even as the mobile terminal moves to a different place, is provided while taking the mobility of the mobile terminal into consideration.
FIG. 1 is a view illustrates handoff in a Wireless Broadband (WiBro) system, which is a mobile communication system, and FIG. 2 is a graph illustrating intensities of signals between a Radio Access Station (RAS) and wireless terminals in the WiBro system. A WiBro system, as shown in FIGS. 1 and 2, includes a plurality of RASs and an Access Control Router (ACR) for controlling the plurality of RASs, wherein a mobile terminal is referred to as a Portable Subscriber Station (PSS).
FIGS. 1 and 2 show a case where a PSS 20 performs a handoff operation from a first RAS (RAS1) 10 to a second RAS (RAS2) 12. Generally, a handoff is performed in such a manner that the PSS 20 continuously monitors the signal intensity between the PSS 20 and each adjacent RAS. Further, when the signal intensity between the PSS 20 and an RAS (i.e., the first RAS 10 in FIG. 1), from which the PSS 20 is currently receiving service, is dropped to a level less than or equal to a predetermined level, the PSS performs a connection to another RAS (i.e., the second RAS 12 in FIG. 2) from which a signal of a higher intensity is received. Practically, a threshold value “T_DROP”, which is for determining whether the signal intensity from an RAS from which service is currently being provided is weak, and a threshold value “T_ADD”, which is for determining whether the signal intensity from an adjacent RAS is strong, are set to be different from each other. Selectively, the PSS may receive service even from an adjacent RAS when the signal intensity from the adjacent RAS is equal to or greater than “T_ADD,” and the PSS may cut off the connection with an RAS from which service is currently being provided when a state, in which the signal intensity from the RAS is less than or equal to “T_DROP”, is continued for a predetermined period of time. An example of such a handoff technology is disclosed in Korean Patent Application No. 2006-0073726, filed on Aug. 4 2006, and which is assigned to the assignee of the present invention.
Meanwhile, in the handoff function, it is important to successfully move a call and to keep the quality of the voice information from being degraded during the handoff process. Accordingly, various methods are being attempted to enable voice information to be transferred without interruption. Also, beginning recently, various methods have been attempted in order to enable information to be transmitted without interruption not only when voice information is transmitted, but also when multimedia data is transmitted.